airforced, you're wrong on this one. All airlines who have added extra legroom seats whether they are designated economy or not are being pursued by HMRC.
The key phrase to note from HMRC is:
Note: If any selection criteria, for seating passengers in the premium cabin or seating, involves extra cost to the passenger for that benefit or the possibility of selection has been offered or advertised prior to the decision to select them, then the operator is deemed to have created more than one class of travel on that aircraft and those passengers are liable for APD at the standard rate.
i.e. if the airline charges extra for the legroom seat then the standard and not the lower rate applies in their eyes.
Some airlines are fighting it, clearly J2 has decided they're onto a hiding to nothing by taking on HMRC and have chosen to remove the seats.
All it will do is result in a poorer product on offer to the public thanks to HMRC.
I might add that they are looking to apply this retrospectively going back 6 years.......